Here's an example of the kind of material you can do in a webcast that's hard to do in broadcast television.
In this interview Nassim Taleb talks about risk and about how most investors underestimate the importance of rare events. A point along the same lines as those made by Benoit Mandelbrot in his recent book.
What's interesting about the interview is that it is long and I would say quite technical really, even if Taleb does not actually throw equations around.
Since distribution cost dominates production cost, that kind of limited audience interviews make little sense for broadcast.
As we immerse ourselves deeper and deeper in a knowledge society, where value comes from specialization, i.e. limited knowledge, we should find most of our interests have this quality: They're much more suited for the world of ends than for anything else. What's disconcerting for broadcasters is that this kind of specialization is even true for entertainment. I read somewhere recently that kids simply aren't watching television anymore, they're playing networked games.